Such sensors are known in which the common electrode is a metal tube surrounding the line conductor, with the second electrode of the auxiliary capacitor being another tube of larger diameter which is separated from the first tube by a dielectric layer.
In such sensors, the capacitance of the high tension capacitor is not stable if ambient temperature varies. The length of the tube constituting the common electrode varies as a function of temperature, thereby disturbing the measurement of the potential of the line conductor beyond the acceptable margin of error which is about 0.2%.
The object of the present invention is to design a capacitive sensor in which the high tension capacitor has high stability. This object is achieved by adding two screens which leave a window between them of size which is constant regardless of temperature.